Manufacture of naphthenic hydrocarbons by hydrogenating the corresponding aromatic hydrocarbons

ABSTRACT

A process of hydronating benzene to cyclohexane, comprising the steps of: A. INTERMITTENTLY CIRCULATING A LIQUID STREAM COMPRISING PARTICULATE HYDROGENATION CATALYST SUSPENDED IN LIQUID BENZENE DOWNWARDLY THROUGH A FIRST ELONGATED ZONE, AND PASSING HYDROGEN UPWARDLY AND COUNTERCURRENTLY TO SAID LIQUID STREAM TO CONVERT SAID BENZENE TO CYCLOHEXANE, THE CONVERSION BEING CONDUCTED AT ABOUT 125*-275* C. and about 5-100 atmospheres under conditions wherein said benzene remains essentially in the liquid phase; B. WITHDRAWING GASEOUS CYCLOHEXANE PRODUCT AND EXCESS HYDROGEN FROM THE TOP OF SAID FIRST ELONGATED ZONE; C. WITHDRAWING RESULTANT HYDROGENATED BENZENE STREAM CONTAINING SAID DISPERSED PARTICULATE HYDROGENATION CATALYST FROM THE BOTTOM OF SAID FIRST ELONGATED ZONE, AND PASSING SAID RESULTANT STREAM DOWNWARDLY THROUGH A SECOND ELONGATED ZONE, SAID SECOND ZONE BEING A HEAT EXCHANGE ZONE COMPRISING A PLURALITY OF TUBULAR PASSAGEWAYS SURROUNDED BY COOLANT FLUID; D. WITHDRAWING RESULTANT COOLED HYDROGENATED BENZENE STREAM FROM THE BOTTOM OF SAID SECOND ZONE AND RECIRCULATING SAME TO THE TOP PART OF SAID FIRST ZONE; AND E. STOPPING THE CIRCULATION OF SAID LIQUID STREAMS INTERMITTENTLY, AND AT LEAST DURING THE PERIOD DURING WHICH THE CIRCULATION IS STOPPED, INJECTING HYDROGEN INTO THE BOTTOM OF THE SECOND ELONGATED ZONE, PASSING UPWARDLY THROUGH SAID TUBULAR PASSAGEWAYS AND SAID FIRST ELONGATED ZONE SO AS TO DIMINISH THE EXTEND OF SETTLING OF SAID PARTICULATE CATALYST WHEREBY PLUGGING OF SAID TUBULAR PASSAGEWAYS IS SUBSTANTIALLY AVOIDED.

United States Patent i 1 I l l [52] US. Cl [Sl] lnt.Cl..... [50] Field of Search [56] References Cited UNITED STATES PATENTS 3,450,784 6/1969 Reilly et al 2,48 l .921 9/1949 Gwynn Inventors Gabriel Jacques Saint Cloud; Alphonse Zuech, Montessori; Alain Convers, Ruell Malmalson; Jacques Paumler, Rueil Malmaison, all ol France Appl. No. 882,054 Filed Dec. 4, 1969 Patented Nov. i6, 197! Assignee lnstltut Francals du Petrole, des

Carburants et Lubrlflants Rueil Malmalson, France Priority Dec. 9, 1968 France 177,338

MANUFACTURE OF NAPHTHENIC HYDROCARBONS BY HYDROGENATING THE CORRESPONDING AROMATIC HYDROCARBONS 5 Claims, 2 Drawing Figs.

Primary Examiner- Delbert E. Gantz Assistant ExaminerVeronica O'Keefe Attornvy- Miller, Raptes & White ABSTRACT: A process of hydronating benzene to cyclohexane, comprising the steps of:

a. intermittently circulating a liquid stream comprising particulate hydrogenation catalyst suspended in liquid benzene downwardly through a first elongated zone, and passing hydrogen upwardly and countercurrently to said liquid stream to convert said benzene to cyclohexane, the conversion being conducted at aboi it l25-275 C. and about 5-100 atmospheres under conditions wherein said benzene remains essentially in the liquid phase;

b. withdrawing gaseous cyclohexane product and excess hydrogen from the top of said first elongated zone;

c. withdrawing resultant hydrogenated benzene stream containing said dispersed particulate hydrogenation catalyst from the bottom of said first elongated zone, and passing said resultant stream downwardly through a second elongated zone, said second zone being a heat exchange zone comprising a plurality of tubular passageways surrounded by coolant fluid;

d. withdrawing resultant cooled hydrogenated benzene stream from the bottom of said second zone and recirculating same to the top part of said first zone; and

e. stopping the circulation of said liquid streams intermittently, and at least during the period during which the circulation is stopped. injecting hydrogen into the bottom of the second elongated zone, passing upwardly through said tubular passageways and said first elongated zone so as to diminish the extend of settling of said particulate catalyst whereby plugging of said tubular passageways is substantially avoided.

PATENTEDNUV 16 ISTI 3,621,068

SHEET 1 0F 2 MANUFACTURE OF NAPHTHENIC HYDROCARBONS BY HYDROGENATING THE CORRESPONDING AROMATlC HYDROCARBONS This invention relates to a process for hydrogenating aromatic hydrocarbons in the liquid phase, by use of a catalyst suspended therein, in at least two elongated and substantially vertical zones located one above the other, the lower zone consisting of a plurality of passageways acting as a heat exchanger, in which process, under normal conditions of operation, comprising a downward liquid circulation through said two zones together with an external recycling, from 70 percent to percent of the hydrogen is fed to the upper zone and from 0 to 30 percent to the lower zone, and, when stopping the liquid circulation, there is injected hydrogen at the bottom of the lower zone, the gases flowing in both cases upwardly.

Preferably, in normal operating conditions, from 95 to 100 percent of the hydrogen is introduced in the upper zone and from 0 to 5 percent in the lower zone.

When the liquid circulation is stopped, it is advantageous to inject l to 100 percent of the hydrogen at the bottom of the lower hydrogenation zone, a portion of the hydrogen being optionally introduced at the bottom of the upper zone.

More particularly the invention relates to an improved 7 process for manufacturing cyclohexane by hydrogenation of benzene, in the liquid phase, and in the presence of a suspended catalyst such, for instance, as Raney nickel. Preferably the total weight of the catalyst present in the liquid phase, in continuous running, is between 2 and 12 percent by weight with respect to the liquid phase.

Preferably the primary zone and the secondary zone are each contained in a metal enclosure respectively referred to as hydrogenation reactor and exchanger, said two enclosures being superimposed and interconnected, on one side directly and on the other side through pipe means comprising at least one liquid circulation means such as a pump and at least one supply means for the catalyst, such as a proportioning pump or an inlet lock chamber.

Preferably the entire unit is secured on a bearing block only at one place, for instance through a fastening collar, the circulation pump being elastically suspended so that the whole and more particularly the external piping be able to expand or contract as a result of heat variations.

Other advantages will be apparent from the following description with reference to the accompanying drawing illustrating by way of example one embodiment of the invention.

The operating conditions for carrying out the reaction of hydrogenation of aromatic hydrocarbons to naphthenic hydrocarbons are variable. They depend mainly on the nature of the hydrocarbon subjected to hydrogenation.

In the case, for instance, of benzene, the temperature may vary between 125 and 275 C., preferably between l70 and 230 C. and the pressure which must be sufficient to maintain a liquid phase, is generally between 5 and I00 atmospheres.

As catalyst there can be used any solid substance having a hydrogenating catalytic activity, more particularly a metal from group VIII of the periodical classification of elements and more preferably nickel. This metal can be deposited on a carrier. Of course, the soimpregnated carrier is divided into small particles in order to be suspended in the liquid phase wherein is injected the hydrogenating gas.

Optionally, if desired, there can be carried out a complementary hydrogenation stage (in addition to that carried out in the two hereabovedefined zones). This complementary stage consists, for example, in passing the vapor outflow from the primary hydrogenation zone through a bed of catalyst, which can be (or not) of the same nature as the suspended catalyst, with the optional presence of additional hydrogen.

In any case, with or without the carrying out of the comple' mentary stage, the hydrogen is advantageously used in excess with respect to the stoichiometrical amount.

There can be taken a portion of the naphthenic hydrocarhon obtained in the liquid form, for instance by withdrawing a portion of the so-cnlled recycled liquid.

Generally the aromatic compound to be hydrogenated is introduced in the primary hydrogenation zone, preferably in totality and at a level higher than that of introduction of the hydrogen containing gas.

Nevertheless at least one portion of said aromatic compound can be introduced at one or more freely chosen points of the circuit.

The invention will be further explained more in detail in the following description of an illustrative nonlimitative embodiment with references to the accompanying drawings wherein:

FIG. 1 is a simplified diagram of a unit operating according to the process of the invention, and

FIG. 2 shows more in detail the inlet lock chamber for the catalyst.

Referring now more particularly to FIG. 1, benzene and the hydrogen-containing gas are respectively introduced through lines 1 and 2 in the primary hydrogenation zone or reactor 3, which contains a liquid phase 4 having suspended therein a catalyst, for instance Raney nickel, said liquid phase being delimited by the reactors walls and the upper gas-liquid interface 5. Through duct 6 are discharged from the reactor the gases issued from the liquid phase which essentially consist of cyclohexane vapors, an excess of hydrogen, if any, and/or gases which are inert with respect to the reaction, inert gases optionally introduced into the reactor in admixture with hydrogen, through line 2.

A stream of recycled liquid issuing from exchanger 7, hereinafter described, is reintroduced at the upper part of reactor 3 through line 13.

The liquid phase flows downwardly to the bottom of reactor 3 and then to the secondary hydrogenation zone 7, also acting as exchanger with indirect contact; the cooling fluid used for the indirect thermal exchange enters the exchanger 7 through duct 8 and flows out therefrom through duct 9.

The exchanger comprises one (or more) additional duct 10, wherethrough is introduced, preferably in an intermittent manner the rest of the total hydrogen amount used in the process, in the form either of pure hydrogen or of a gaseous mixture containing the same. Said exchanger may also be provided with other ducts (not shown in the figure) for optional injection of benzene in the case where the total amount thereof is not introduced into the unit through line 1.

The liquid phase, after passage through exchanger 7 where it is cooled down, is returned to reactor 3, preferably at a level v lower than interface 5, through line 11, pump 12 and line 13.

A lock chamber 14 with its two related pairs of valves 15 and 16, provides for introduction of fresh catalyst in the circuit, said lock chamber being described more in detail in FIG. 2. It can be seen from FIG. 1 that the liquid with the solid catalyst suspended therein runs in a closed circuit passing through reactor 3, exchanger 7 and therefrom through lines ll and 13 which close the loop.

This liquid phase essentially consists of benzene and cyclohexane and the added catalyst.

The process is carried out preferably with a low proportion of benzene in said liquid phase, for instance with a ratio by weight of benzene to cyclohexane which is lower than 0.001/1. As a matter of fact, it has been observed that, by this way, there were obtained very high conversion rates together with a substantially complete disappearance of byproducts.

The heat evolved in the hydrogenation reaction is eliminated in the exchanger 7. This exchanger is of a known type, generally comprising an enclosure containing a series of tubes arranged in parallel and wherein circulates the liquid phase to be cooled, issuing from the primary hydrogenation zone. Around these tubes circulates the cooling fluid, for instance water, a portion of which is generally vaporized.

The injection of a complementary amount of hydrogen, through line l0, is advantageously carried out in the outlet collector at the base of the exchanger, for instance through a distributor.

By this way, the hydrogen-containing gas is substantially evenly distributed through the tubes of the exchanger. Of

course any other equivalent introduction device can be uwd, or, although it is less preferred, the hydrogencontaining gas can be introduced directly in one or more tubes of the exchanger.

If, for any reason, it is necessary to stop abruptly the liquid circulation through the circuit, the catalyst grains will settle at the base of reactor 3 and more particularly in exchanger '7, which, in view of the design thereof, is very troublesome. As a matter of fact, the grains will accumulate in the tubes of relatively small diameter of the exchanger and this will involve the risk of impeding or even precluding the reestablishment of the liquid circulation.

The additional hydrogen injection through line it), even at a very small rate as compared to the flow rate through line 2, prevents the accumulation of the catalyst grains in the tubes of the exchanger whereby an immediate starting up is anew possible. Once the liquid circulation is reestablished the hydrogen injection through line can be stopped, if so desired.

However, if maintained, said injected hydrogen provides for a further increase of the cyclohexane yield. The hydrogen amount introduced in exchanger 7 is very low. For example over a complete cycle (i.e. the period of time between two complete stoppages for discharge of the used up catalyst and charge of fresh catalyst), it amounts to less than 30 percent and in most cases lam than 5 percent of the total hydrogen introduced in the circuit.

This additional hydrogen amount depends mainly on the frequency of the partial stopping and/or on the maintenance (or not) of the hydrogen injection in the secondary hydrogenation zone during the non-nal operation of the unit,

There can be maintained, for example, a very low hydrogen rate in the secondary zone during the operation of the unit, said rate being increased during the periods of occasional stoppings.

The injection of catalyst during a cycle may be carried out continuously or intermittently, preferably in conformity with the process described in the French Pat. No. 1,549,207 filed on 24th Mar. 1967.

This last-mentioned process consists of starting one cycle with a limited amount of catalyst, of continuously or intermit tently introducing an additional amount of fresh catalyst up to a maximum catalyst content of the liquid phase, and then of continuing the injection of the fresh catalyst while withdraw ing a substantially equivalent amount of used up catalyst.

PK}. 2. shows more in detail the inlet lock chamber for the catalyst. it must be emphasized that this apparatus is preferred to other systems for introducing the catalyst in the circuit. However any equivalent device may also be used.

The lock chamber M is fed through a catalyst inlet duct l7 provided with the first pair of valves and the catalyst is discharged through a line llil connecting the lock chamber to line ll of the circulating liquid. Said line R8 is provided with the second pair of valves.

Through line l9 cyclohexane is introduced into the lock chamber.

This line has a bypass provided with a flowmeter 20, for instance a rotamcter and a valve 21. Line 119 itself is provided with two valves 22 and 36).

Through line 23 and its pair of valves 2 a hydrogen-containing gas can be injected into the lock chamber. This line is provided with a waste pipe 2'7 having a pair of valves 26. To said waste pipe is connected a balancing pressure line 25. A relief pipe 28 provided with a pair of valves 2d and a pressurerneasuring apparatus P, is connected to line 19.

The device is operated as follows:

All the valves being closed, except pairs l5 and 26 and valves 22 and 30, the lock chamber is filled with cyclohexane up to level H; once this level reached cyclohexane flows out from the unit through line 27 and is recovered in a container 31 provided for this purpose (the curved portion of line .25 has for object to equalize the liquid pressures in this line and the lock chamber so as to prevent a complete siphoning of the cyclohexane out of the lock chamber).

Valves 22., 2'35 and 3'1) are then closed and there is introduced through line 17, a charge of catalyst. Valves 22 and 3th are thereafter again opened so as to completely fill the lock chamber with liquid (this can be easily checked by observing for instance the liquid rising in line l7).

Then the valve 15 is closed and pressurization of the lock chamber is indicated by manometer 115. The pair of valves 16 is then opened while maintaining a flow through line if so as to keep a slight pressure excess in the lock chamber as compared to the pressure of the liquid circulating through line it (pressure excess checked by means of manometer P),

The catalyst progressively flows through line ll. if the flow is stopped, for instance due to a sticking in the bottleneck there is injected hydrogen by opening the pair of valves 24. As soon as the catalyst circulation is reestablished, it is preferable to close the pair of valves 24. to

in order to be sure that all the catalyst has passed through line ill the following test is conducted: valve 21 is opened while valve 22 is progressively closed. The indication of an abrupt increase of the flow rate, as read on flowmeter 20, shows that the catalyst has been transferred.

The valves lb, 21 and Bill are then closed and the lock chamber depressurized by opening of the valve pair 29. Line 23 is advantageously connected to the flare of the unit. Cyclohexane is then returned to the lock chamber at level H by opening of valve pair 26. Valve pairs 26 and 29 are closed. The lock chamber is again in position to receive a new charge of catalyst.

This device offers numerous advantages, in particular line replaces a known device consisting of a glass level which is clogged very quickly. The control of the steadiness of the catalyst injection and of the end of this injection is achieved by reading rotatometer 2i).

Moreover it is preferable to provide a valve operator (particularly for pairs l5 and 16) so arranged that the 4 valves could not be simultaneously in open position (for example with two operating handles which cannot be cleared as long as the valves are in closed position).

This arrangement avoids to discharge to atmosphere a circulation liquid containing in suspension a generally pyrophoric catalyst, which involves many risks.

There can also be used, for withdrawing the used up catalyst from the circuit, a lock chamber (not shown in HO. 1) called outlet-lock chamber and operating in a similar way as the said inlet-lock chamber 114.

What we claim as this invention is:

l. A process of hydrogenating benzene to cyclohexane, comprising the steps of:

a. intermittently circulating a liquid stream comprising particulate hydrogenation catalyst suspended in liquid benzene downwardly through a first elongated zone, and passing hydrogen upwardly and countercurrently to said liquid stream to convert said benzene to cyclohexane, the conversion being conducted at about 275 C. and about 5-100 atmospheres under conditions wherein said benzene remains essentially in the liquid phase;

b. withdrawing gaseous cyclohexane product and excess hydrogen from the top of said first elongated zone;

c. withdrawing resultant hydrogenated benzene stream containing said dispersed particulate hydrogenation catalyst from the bottom of said first elongated zone, and passing said resultant stream downwardly through a second elongated zone, said second zone being a heat exchange zone comprising a plurality of tubular passageways surrounded by coolant fluid;

d. withdrawing resultant cooled hydrogenated benzene stream from the bottom of said second zone and recirculating same to the top part of said first zone; and

e. stopping the circulation of said liquid streams intermittently, and at least during the period during which the circulation is stopped, injecting hydrogen into the bottom of the second elongated zone, passing upwardly through said tubular passageways and said first elongated zone so as to diminish the extent of settling of said particulate catalyst whereby plugging of said tubular passageways is substan tially avoided.

2. A process according to claim 1 wherein from 95 to 100 percent of the hydrogen is introduced in the upper zone and from to percent in the lower zone, under normal operating conditions.

3. A process according to claim 1, wherein, when stopping the liquid circulation, from 1 to 100 percent of the hydrogen is injected at the base of the lower zone.

4. A process according to claim 1, wherein, when stopping UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 2 0 Dat November 16, 1971 Inv n ofls) Gabriel Jacques et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Attorney of Record:

Please correct the firm name to read --MILLEN, RAPTES & WHITE---;

In the Abstract;

Please amend the Abstract as follows:

Second to the last line, "extend" should be ---extent---;

In the Claims:

Please amend the claims as follows:

Claim 1, line 8, change "125 275C to read ---125-275C-- Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTI'SCHALK Attesting Officer Commissioner of Patents ORM PO-IOSD (10-69) USCOMM-DC 60376-P09 at us, covzmmzm rnm'rmn OFFICE n09 o-asl-au 

2. A process according to claim 1 wherein from 95 to 100 percent of the hydrogen is introduced in the upper zone and from 0 to 5 percent in the lower zone, under normal operating conditions.
 3. A process according to claim 1, wherein, when stopping the liquid circulation, from 1 to 100 percent of the hydrogen is injected at the base of the lower zone.
 4. A process according to claim 1, wherein, when stopping the liquid circulation, one portion of the hydrogen is introduced at the bottom of the lower zone and one portion at the bottom of the upper zone.
 5. The process of claim 1, wherein hydrogen is also injected at the bottom of said second elongated zone when the liquid stream is normally circulated through both zones, from 70 to 100 percent of the total hydrogen being introduced into the first elongated zone and from 0 to 30 percent in the second elongated zone. 